1. Field of the Disclosure
Embodiments of the present invention relate to a display device and a touch sensing method thereof, and more particularly, to a display device integrated with a touch sensor and a touch sensing method thereof.
2. Discussion of the Related Art
With a development of various portable electronic devices such as a mobile phone and a notebook computer, a demand for flat display devices to be applied to the various portable electronic devices has been increased steeply.
For example, the flat display devices may include a liquid crystal display device, a plasma display panel, a field emission display device, a light emitting diode display device, and an organic light emitting diode display device.
Among the above flat display devices, an application of the liquid crystal display device is gradually increased owing to advantages of mass production technology, easy driving, high quality image with good resolution, and large-sized screen. Furthermore, a liquid crystal display device having a touch screen has attracted great attentions, wherein the liquid crystal display device having a touch screen facilitates to directly input information to a screen through the use of finger or pen.
When the touch screen is applied to the liquid crystal display device, the related art inevitably needs a touch panel additionally provided on a liquid crystal panel. Recently, in accordance with a demand for slimness, a liquid crystal panel integrated with a touch screen has been developed.
Especially, an in-cell touch type liquid crystal display device has been actively studied, wherein a common electrode formed on a lower substrate is used as a touch sensing electrode.
In case of the in-cell touch type liquid crystal display device, a pixel for displaying an image is formed together with a touch screen for sensing a user's touch, whereby displaying an image and sensing touch are separately driven by a time division method due to the above structural properties.
If there is a user's touch during a touch sensing period (non-display period), a capacitance change occurs in a touch sensing block with the user's touch, and a touch sensing electrode senses the capacitance change, to thereby sense whether or not there is a user's touch.
According to the related art, when a touch sensor is formed outside the liquid crystal panel, a displaying driving mode and a touch sensing driving mode are separately performed so that the respective modes are not affected. However, if the touch sensor is provided inside the liquid crystal panel, the respective modes might be mutually affected.
That is, the touch sensing driving may be affected by the displaying driving, or the displaying driving may be affected by the touch sensing driving. This will be described in detail with reference to Figure (FIG.) 1.
FIG. 1 illustrates capacitance changes of a pixel for displaying black and a pixel for displaying white in an in-cell touch type liquid crystal display device according to the related art.
As shown in FIG. 1, an alignment of liquid crystal in the pixel for displaying black (black) is different from an alignment of liquid crystal in the pixel for displaying white (white), whereby a capacitance difference (Cm_w−Cm_b) of a liquid crystal layer occurs.
The capacitance difference between the pixels remains in the pixels even after a start of the touch sensing period, whereby the touch sensing may be affected by the capacitance difference. The capacitance difference serves as “off-set”, that is, noise in touch sensing, which is referred to as “DTX: Display Touch Crosstalk”.
This display touch crosstalk may deteriorate touch accuracy and stability.